Manually Adjusting the Tax field

I am using MYOB Business Pro.

When creating an Invoice, why can't MYOB add a simple feature that allows you to manually adjust the Tax field to reflect the exact GST amount on a invoice?

It would save customers significant time in adding description lines for GST-free items, and working out what portion of services/disbursements are GST-free.

This feature was available on primitive desktop versions, but why not on the current web versions in this modern day. Surely MYOB knows that not all services/items in Australia have GST, there are GST-free items, or a combination of GST/GST-free items too.

Frustrated at the lack of development for a major accounting software provider.